The present invention relates to a low vibration blasting method of bench rock with two free surfaces and a general blasting method of bench rock with two free surfaces. As used herein, the term xe2x80x9clow vibration blasting method of a benchxe2x80x9d means a blasting method of a bench of rock, which is conducted at reduced charge amounts per delay after holes are drilled with leg drills of a small bore (i.e., about 38 mm diameter) so as to have a relatively short drilling length and a relatively narrow drilling interval. The term xe2x80x9cgeneral blasting method of a benchxe2x80x9d means a large-scale blasting method of a bench of rock, which is conducted with a large amount of explosives after holes are drilled with crawler drills of a large bore (1.e., about 45 mm to 75 mm diameter) so as to have a relatively long drilling length and a relatively drilling interval.
FIG. 1a is a plane view showing a general structure of a bench of rock with two free surfaces, and FIG. 1b is a cross-sectional view taken along the line A-Axe2x80x2 in FIG. 1a. As shown in FIGS. 1a and 1b, the bench of rock has two free surfaces, an upper free surface 1 and a slant free surface 2 extended slantly from the upper surface 1. In addition, the bench of rock has a given width 3, a given length 4 and a given height 5.
Conventionally, multiple blasting holes are drilled along a surface of a bench having two free surfaces, at regular intervals, generally at intervals corresponding to 1.2 times as large as a burden, and then charged with explosives. Thereafter, one blasting hole positioned at a central portion of the bench is blasted first so as to form a third free surface, and then blasting holes arranged at the left and right sides of the central hole are blasted. Such a blasting mechanism is applied for the low vibration blasting of bench and the general blasting of bench, in the same manner. In this case, although blasting vibration and blasting noise can be reduced by changing the charge amounts per delay depending on the drilling interval and depth, the control of the charge amounts per delay under the same conditions has limitations.
In order to reduce blasting nuisances, such as blasting vibration, blasting noise, air overpressure, fly rock and the like, a blasting mechanism is required, by which optimal blasting is carried out at minimized charge amounts per delay, and the number of free surfaces is increased by regulation of the blasting sequence.
Blasting methods of bench of two free surfaces, which are widely employed nowadays, can be classified according to drilling form into a downward drilling type and a horizontal drilling type. Also, according to application, they can be classified into a general blasting method of bench carried out at an area having no connection with blasting nuisance, and a low vibration blasting method of bench conducted in the vicinity of a sensitive structure or a stall for reduction of blasting nuisance.
The blasting method of the vertical drilling type is a method that is mainly used for blasting an open-air bench with two free surfaces. In this method, as the main drilling direction is vertical or slanted downward from ground, large-scale blasting operations can be carried out by employing equipment to the maximum level. Thus, this method is applied for blasting of bench in a quarry or a working area for large-scale cutting, etc. On the other hand, the blasting method of the horizontal drilling type is mainly applied for blasting of benches in underground caves or tunnels at which holes must be horizontally drilled in view of working conditions. Thus, it is inferior to the vertical drilling type in productivity so is not particularly used except in special cases.
FIG. 2a is a plane view showing a downward drilling pattern according to the prior general blasting method of bench, and FIG. 2b is a cross-sectional view taken along the line A-Axe2x80x2 of FIG. 2a. As shown in FIGS. 2a and 2b, plural blasting holes 6 are formed downward on the upper free surface 1 of the bench in a direction parallel to the vertical or slant free surface 2, charged with explosives and then blasted. The method illustrated in FIGS. 2a and 2b has high productivity as it makes large-scale blasting possible. Thus, it is mainly used in a large-scale quarry or a working area for large-scale cutting. In addition, in order to make the upper free surface even, sub-holes 8 may also be drilled and blasted. However, it requires additional drillings and charges and thus is used only for special cases.
FIG. 3a is a plane view showing a horizontal drilling pattern according to the prior general blasting method of bench, and FIG. 3b is a cross-sectional view taken along the line A-Axe2x80x2 of FIG. 3a. As shown in FIGS. 3a and 3b, blasting holes 9 are drilled at the vertical or slant free surface 2 of the bench in a direction parallel to the upper free surface 1, charged with explosives and then blasted. The method shown in FIGS. 3a and 3b is mainly used for blasting of benches in tunnels or underground caves.
Furthermore, the low vibration blasting method of bench according to the prior art utilizes the same blasting concept as that of the general blasting method of bench. In this low vibration blasting method, however, in order to reduce blasting nuisance, blast holes are drilled so as to have a short drilling interval and length, and are blasted with a small amount of explosives. According to this low vibration blasting method of bench, blasting nuisance can be limited. However, this method is disadvantageous in that blasting costs are expensive.
In the blasting method of bench according to the prior art, the downward holes 6 or the horizontal holes 9 are collectively drilled at the upper free surface 1 or the slant free surface 2 in one side direction. Then, as shown in FIG. 4, rod-like charge or deck charge is carried out. In this charge process, a primer cartridge 35 is placed in an indirect priming manner, a middle priming manner or a direct priming manner. Then, the bench is blasted on two free surfaces so that only the blasting effect forms a third free surface in a blasting process. As used herein, the term xe2x80x9cindirect priming mannerxe2x80x9d means that primer cartridge 35 is placed at the bottom portion of the hole, and an explosive 36 is placed above the primer cartridge 35, as in the left hole 32 in FIG. 5. The term xe2x80x9cmiddle priming mannerxe2x80x9d means that the primer cartridge 35 is placed at a middle portion of the hole, and an explosive is placed at the upper and lower portions of the primer cartridge 35, as in the middle hole 33 in FIG. 5. The term xe2x80x9cdirect priming mannerxe2x80x9d means that the primer cartridge 35 is placed at the entrance to the hole, and an explosive is placed below the primer cartridge 35, as in the right hole 34 in FIG. 5. Also, in FIG. 5, the reference numeral 38 denotes a tamping.
Blasting of a bench with two free surfaces is mostly carried out in an open air area, and may have an influence on the surrounding area, such as private houses, buildings, stalls and fishing places, etc. For this reason, it requires special attention.
Examples of blasting nuisances occurring upon blasting in an open air area include blasting vibration, blasting noise, air overpressure, fly rock and the like. The reason for the blasting nuisance is because significant portions of the explosive are lost into the vibration, noise, heat and light, etc., upon detonation of the explosive in the drilled rock, by a powerful chemical reaction in which great energy is released in a short time. For this reason, the surrounding rock or structure may be damaged due to the blasting nuisances.
Therefore, in order to solve the above-mentioned problem caused by blasting nuisance, the number of cracks and free surfaces need to be increased as much as possible such that much explosive energy of the explosives may be applied in fracturing rock, whereby optimal blasting can be performed.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a blasting method of a bench of rock, by which blasting nuisance can be reduced and blasting efficiency increased.
It is other object of the present invention to provide a blasting method of a bench of rock, by which the size of fractured rock can be controlled while blasting nuisance can be reduced and blasting efficiency increased.
It is another object of the present invention to provide a blasting method of a bench of rock, by which a bottom surface of blasted base rock can be level and at the same time, reducing blasting nuisance and increasing blasting efficiency.
It is also another object of the present invention to provide a blasting method of a bench of rock, which can be conducted so as to coincide with field conditions, and by which blasting nuisance can be reduced and blasting efficiency increased.
It is still another object of the present invention to provide a blasting method for the excavation of rock, by which initial blasting of a first free surface can be achieved, and at the same time, reducing blasting nuisance and increasing blasting efficiency.
It is yet another object of the present invention to provide a blasting method of a bench of rock, by which a slope can be formed, and at the same time, reducing blasting nuisance and increasing blasting efficiency.
To accomplish this object, there is provided a blasting method of rock, which utilizes a blasting mechanism comprising the steps of: successively drilling a plurality of blasting holes on a upper free surface of a bench of rock with two free surface consisting of the upper free surface and a slant free surface extended from the upper free surface or on a free surface of rock with one free surface, in which the blasting holes are arranged in a straight line and consist of a first group of first-order blasting holes, a second-order blasting hole and a second group of first-order blasting holes; charging the blasting holes with an explosive; blasting the first-order blasting holes so as to form four free surfaces around the second-order blasting hole; and blasting the second-order blasting hole in a state where the four free surfaces were formed. In the blasting mechanism according to the present invention, the first-order blasting holes consist of either two presplitting holes, or two presplitting holes and one delay blasting hole placed between the presplitting holes, or presplitting holes and/or delay blasting holes of any number or drilling pattern, that can be blasted with small amount of explosives and low vibration and allows formation of four free surfaces around the second-order blasting hole.
According to the blasting method of the present invention, after the first-order blasting process is conducted using a reduced charge amount per delay, the second-order blasting process is carried out in a state where four free surfaces were formed as a result of the first-order blasting. Therefore, in the blasting method of the present invention, blasting efficiency can be increased, and blasting nuisances, such as blasting vibration and blasting noise, etc., can be significantly reduced.